Despite the known benefits of physical activity, nearly 70% of American adults do not engage in regular leisure-time physical activity. A better understanding of the theoretical determinants of physical activity is necessary to improve intervention outcomes. Although the impact of affective responses to exercise on future physical activity behavior has received little research attention, learning theory, social learning theory, and response expectancy theory 3rovide theoretical guidelines for understanding how affective responses to physical activity may operate in determining physical activity behavior. The overall goal of the proposed study is to explore the role of affective variables as determinants of future physical activity behavior through: (1) analyzing existing data on affect and exercise from NIH-funded projects; (2) examining affective variables among participants in an ongoing NIH-funded project; and (3) examining theory-based hypotheses in the context of a small lab-based study. Taken together, the proposed research will help to advance our knowledge of the theoretical determinants of physical activity, which will aid in the improved design of future interventions.